This invention relates generally to air conditioning and heat pump systems and more particularly to method and apparatus for controlling the amount of heating or cooling capacity of these systems.
Air conditioning and heat pump systems are commonly driven by a plurality of heating or cooling stages that are selectively activated by a control system in order to achieve a desired amount of heating or cooling capacity. One approach to achieving desired heating or cooling capacity has been to sequentially activate stages until a desired temperature is achieved in the space to be heated or cooled. Another approach has been to selectively activate stages according to which stage has been idle for the longest period of time. Still another approach has been to first calculate the number of stages that will be needed to heat or cool an area to a desired temperature and then only activate that number of stages. This latter approach has been heretofore premised on providing the control system in advance with a predetermined gain value for each stage within the system. This gain value represents the nominal rise or drop in temperature that a given stage will contribute to the total rise or drop in temperature of the media to be heated or cooled. The control system calculates the differential in temperature between the current and desired temperature of the media to be heated or cooled. The control system thereafter proceeds to divide this differential by the aforementioned gain value per each stage. The result is the number of stages that need to be activated to achieve the desired temperature.
It is to be appreciated that the aforementioned calculation of number of stages to be activated is premised on the gain per stage value not varying significantly. This premise cannot be assured under certain circumstances. Specifically, this gain value will vary as a function of the temperature changes or air flow experienced by the condenser or the evaporator within the air conditioning or heat pump system in which the stages are operating. These changes in temperature will in turn affect the pressure differential across a compressor in each activated stage. This may produce a significantly different contribution by each stage to the total system gain than had been previously assumed.